1. Field of the Invention
The present invention relates to a molding chamber for green sand cakes. More particularly, the present invention is directed to a variable-volume molding chamber that reduces the consumption of sand used in making the cake, by minimizing dimensions of the molding chamber used in making the cake.
2. Discussion of Related Art
In conventional sand cake molding machines used for casting, a tubular chamber is formed that has a generally rectangular in cross section. The chamber is closed at one end by a movable, wall, one that is pivotably mounted to permit the egress of the cake once the cake is molded. At the other end it is closed by an end wall that is moved by a piston for implementing compacting and subsequent expulsion of the cake. Thus, the conventional sand molding chamber has four fixed walls constituting the tubular body, including an upper one having a mouth or orifice through which the sand enters, and two movable end walls, corresponding to the six faces formed on the cake by the sand molding chamber,
More specifically, as is illustrated in the different molding steps shown in FIG. 1, the sand cavity is formed when the two movable walls are separated by a suitable distance (first step), the movable walls then move towards each other for compacting the sand cake (second step), the pivotable movable wall subsequently is displaced outwards longitudinally and then tilted upwards to permit the cake to pass freely out of the sand molding chamber (third step), following which the movable wall displaced by the piston moves until it comes into contact with that pivotable wall (fourth step), the piston returns to its initial position while the filling of the mold provided by the sand takes place (fifth step), and finally the pivotable wall descends and is displaced longitudinally until, in the (sixth step), it is in the position shown in the first step, and the sand molding process begins once more.
Thus, given that both the upper and lower walls, and the side walls of the conventional sand molding chamber are fixed, although the smaller castings that are made using the sand molding chamber would theoretically permit the use of smaller sand cakes that use less sand, this is not possible. The entire sand molding chamber that is used for making larger castings must be filled with sand, regardless. This unnecessary use of larger sand cakes is costly. For example:
1) Because the amount of sand that is available in the factory is a finite number of tons the amount of sand available is a fixed constraint on the feasible production rate of the casting machine. That is, in accordance with the invention, the sand molding chamber of the casting machine may be capable of producing more cakes than was possible for machines having conventional mold-making chambers, given the finite quantity of sand available in the casting shop.
2) After the casting process the sand mold is destroyed and the sand has to be treated to remove impurities. That processing incurs costs and times that increase as the amount of sand being processed increases.
The invention provides green sand cake molding chambers that overcome the aforementioned problems in an entirely satisfactory manner.
In accordance with the invention a molding chamber having a variable volume is provided, permitting the volume of sand being used to adjust to the individual dimensional requirements of each type of cake being formed, particularly by reducing to a theoretical minimum requirement the actual maximum dimensions used in the sand molding chamber. Specifically, walls of the chamber that are fixed in place in conventional sand molding chambers, are formed of respective movable plates, is movable plate is mounted on a plate-holder fame, and the plate-holder frames are moved by the push rods of respective hydraulic cylinders. Guides cooperating with the plate-holder frames are conveniently mounted on a support so as to ensure correct displacement of the plates in their closing and opening movements.
The two movable end walls each have replaceable plate assemblies. Each replaceable plate assembly includes a pattern plate having a width that varies depending upon the width of the sand cake required by the pattern. The width of the sand cake is variable between a maximum measurement and a minimum measurement, the maximum measurement corresponding to the greatest width the mold-making chamber of the casting machine can produce and a minimum measurement being limited by the width of a faceplate on which the plate-holder frame is mounted. A pattern plate is fastened to each plate-holder frame, preferably by screws, and the plate-holder frame is fastened, preferably by means of pneumatic clamps, to each faceplate, one faceplate being fixed to the pneumatic compacting cylinder and the other faceplate being pivotably mounted to a displaceable hinge arm that permits the mold-making chamber to open.